Re: Building Pinhole Cameras
tomf2468@pipeline.com
Mon, 5 Aug 1996 20:16:51 GMT
In pinhole work, as in lens photography, the F-stop is simply focal
length/aperature. If you have a 2 inch focal length and a 1 inch aperature
then you have a 2/1 or F2. If you have a 0.5 inch aperature then you have
2/0.5 or F4. The same with pinhole, if you use my (previous) example of
3.5 inch focal length and 0.0135 aperature (pinhole diamiter) then you have
3.5/0.0135 or F259 (I think I rounded this to F260 in my last post).
As to "focal length" (pinhole to film distance in pinhole work), the
previous posts formula "Hole (inches)= square root of focal length/141, in
mm=square root of focal length/28.4" dictates this (for optimal sharpnes.
This formula can be reworked (if you are starting with a known hole size,
as opposed to a known focal lenght) as: Focal Lenght in inches = (hole
diamiter x 141) squared. So... If your camera is 4' focal lenght, then
hole = (square root of focal length)/141, or hole = (square root of 4)/141
or hole =
0.0142 inches in diamiter (for optimal sharpnes). I would try something
like 0.02 to 0.025 inches (about a #75 or #73 drill), because I don't want
optimal sharpnes!! (see earlier post).
On Mon, Aug 5, 1996 11:40:29 AM, Macy Garcia wrote:
>Also, the f-stop is used to calculate your exposure, but what about the
>distance from pin hole to film/paper? My camera is only 4" from pin hole
>to film.
>
>Thanks again
>